Vibrator system for generating seismic waves in the earth

ABSTRACT

This invention describes a vehicle-mounted electrohydraulic vibrator system useful for generating seismic waves in th earth. It comprises a baseplate supported from the vehicle by downwardly extending means and attached to the baseplate through compliances. The vibrator system comprises four hydraulic cylinders and pistons operatively mounted in the cylinders. The pistons are attached to the baseplate through a first frame and are supported thereby. The cylinders are connected to a second frame placed above and resting on the vibrator. The second frame is adapted to support a mass. The mass can be a separate discrete mass of metal, or alternatively, the second frame can be clamped to the bed of the vehicle, in which case the vehicle becomes the reaction mass. If the vehicle has a drive shaft, two of the cylinders are placed on each side of the drive shaft. The pistons in the cylinders are single-acting. That is, a first piston in a first cylinder is pushed downwardly and a second piston in a second cylinder is pushed upwardly with respect to the cylinders when pressure fluid is introduced into the cylinders. The four single-acting vibrators arranged in rectangular spacing provide an alternating vertical force acting at the center of the rectangle.

United States Silver-man atent 1 Feb. 5, 1974 SEISMIC WAVES IN THE EARTHDaniel Silverman, 5969 S. Birmingham, Tulsa, Okla. 74105 221 Filed: Feb.7, 1972 211 Appl. No.: 223,896

[76] Inventor:

Primary Examiner--Samuel Feinberg Assistant Examine'rJ. V. Doramus [5 7]ABSTRACT This invention describes a vehicle-mounted electrohydraulicvibrator system useful for generating seismic waves in th earth. Itcomprises a baseplate supported from the vehicle by downwardly extendingmeans and attached to the baseplate through compliances,

The vibrator system comprises four hydraulic cylinders and pistonsoperatively mounted in the cylinders. The pistons are attached to thebaseplate through a first frame and are supported thereby. The cylindersare connected to a second frame placed above and resting on thevibrator. The second frame is adapted to support a mass. The mass can bea separate discrete mass of metal, or alternatively, the second framecan be clamped to the bed of the vehicle, in which case the vehiclebecomes the reaction mass. If the vehicle has a drive shaft, two of thecylinders are placed on each side of the drive shaft.

The pistons in the cylinders are single-acting. That is, a first pistonin a first cylinder is pushed downwardly and a second piston in a secondcylinder is pushed upwardly with respect to the cylinders when pressurefluid is introduced into the cylinders; The four single-acting vibratorsarranged in rectangular spacing provide an alternating vertical forceacting at the center of the rectangle.

24 Claims, 13 Drawing Figures VIBRATOR SYSTEM FOR GENERATING SEISMICWAVES IN THE EARTH DESCRIPTION OF THE PRIOR ART The prior art isrepresented by the following US Pats., Nos. 2,910,134 Crawford et al.;3,159,233 Clynch et al.; and 3,306,391 Bays.

In the geophysical exploration industry using the seismic method ofmapping subsurface geology, there has been, in recent years, an increasein the use of a method of seismic prospecting called the Vibroseissystem. This method, unlike the conventional explosive impulse method,uses a vibratory signal involving many cycles of alternating pressureagainst the surface of the earth. The frequency of the alternationsgenerally varies with time, the signals being called swept frequencysignals, which typically have a duration of from to 7 seconds, and afrequency range of from 20-100 cps.

This swept frequency seismic signal in the earth is generated by anelectrohydraulic vibrator supported on a baseplate which is pressed intocontact with the earth by a portion of the weight of the truck or othervehicle which transports the vibrator. The vibrator comprises acylindrical mass (of weight up to 5,000 pounds) with a cylindrical borecontaining a piston. Piston rods extend above and below the piston andare attached to a frame which surrounds the mass and is supported on thebaseplate.

The vibrator is generally mounted near the middle of the truck or othertransport vehicle. Those vehicles, such as trucks, which have a driveshaft, require that the vibrator be mounted on a tall structure, ortower, which is attached to the base plate, the legs of which straddlethe drive shaft. The vibrator is mounted on top of the tower, where itis generally at an elevation above the bed of the truck. This large massmounted on the high tower provides an unstable condition, and is aweakness of the prior art designs. Also, the large mass of the toweradds to the mass of the moving system and detracts from the oscillatingforce that can be applied to accelerate the earth. It is well known thatone measure of the energy transmitted into the earth is the amplitude ofmotion of the baseplate. Also, the amplitude of motion of the movingsystem comprising piston, piston rods, frame, tower and baseplate for aconstant force input, varies inversely to the mass of the moving system.Therefore, any excess mass in the moving system detracts from the forcethat can be applied to accelerate the earth.

SUMMARY OF THE INVENTION It is a primary object of this invention toprovide an electrohydraulic vibrator for mounting on a vehicle with adrive shaft, wherein the vibrator is mounted at low elevation, directlyon the baseplate.

It is a further object of this invention to provide a seismic vibratorwhich has a moving system of minimum mass.

It is a still further object of this invention to provide a seismicvibrator in which a separate reaction mass for the vibrator is notrequired, but in which the mass of the vehicle serves both as ahold-down mass and as the reaction mass for the vibrator.

It is a still further object of this invention to provide a vibratorsystem in which a plurality of vibrators are operated in parallel andwhich include means to accurately synchronize all of the vibrators so asto be precisely in-phase.

It is a still further object of this invention to provide a vibratorsystem that has a higher frequency of operation than conventionalsystems.

These and other objects are accomplished and the limitations of theprior art devices are overcome in the design of the present invention,in which four short vertical hydraulic cylinders are used, with foursingleacting pistons slidably received therein. The four cylinders arepositioned two on each side of the drive shaft in the corners ofarectangle. Two of the cylinders, (on a diagonal of the rectangle) areoriented so that on the application of hydraulic pressure, the pistonsmove upwardly, and in the other two, (on the other diagonal) the pistonsmove downwardly, with respect to the cylinders. The thickness of thecylinder walls is no greater than that required for pressure andmechanical requirements, as the mass is not directly associated with thecylinders, as in the prior art.

There is a first frame to which the extended ends of the pistons areconnected. There is a second frame to which the cylinders are connected.Either the first or second frame can be connected to the baseplate, inwhich case the other frame is connected to the mass. In order tominimize the mass of the moving system, the first frame, (connected tothe pistons) is preferably connected to the baseplate, and the secondframe (connected to the cylinders) supports the mass above thecylinders. The axes of the cylinders are parallel to each other andperpendicular to the baseplate.

In this design of the vibrator, the pistons and cylinders aresubstantially less than half as tall as the cylinder in the prior art.Also, because two pistons push in parallel and two pull in parallel,they can be of smaller diameter. The mass of the first frame, pluspistons and baseplate, which constitute the moving system, is thus verymuch less than that of the prior art systems. Therefore, a much smallerforce is required to accelerate the moving system, leaving a largerfraction of the total force output of the vibrator to accelerate theearth and to generate seismic waves. Furthermore, the lighter masspermits higher frequency of operation. Also, as will be described later,since the cylinders are smaller, the fluid volume to each cylinder issmaller, and conventional valves will provide a higher frequency ofoperation. These are some of the principal operating benefits of thisinvention.

' Considering that the first frame connects the pistons to thebaseplate, then the second frame connects the cylinders to the mass. Themass can be a separate discrete volume of metal mounted on the secondframe. However, since there is a practical limit to the weight of such amass that can conveniently be transported, in this invention the mass ofthe vehicle is used both to press the baseplate into firm contact withthe earth, and to provide the reaction mass for the vibrator. The secondframe extends upwardly to the level of the truck bed, and after thebaseplate has been positioned on the earth and the truck frame raised,the second frame is removably clamped to the truck bed. One way to dothis provides a vertical post, as part of the second frame, with aplurality of hydraulic rams attached to the truck frame that moveradially inwardly to grasp the post and hold it rigidly in associationwith the frame of the truck.

The preferred design makes use of four single-acting pistons in shortcylinders, two on each side of the drive shaft. However, it is possibleto use two cylinders, one on each side of the drive shaft withdouble-acting pistons. Here again, the pistons are attached to the firstframe, the cylinders to the second frame and the second frame clamped tothe truck frame.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of thisinvention and a clear understanding of the principles of the inventionwill be evident from the following description taken in conjunction withthe appended drawings, in which:

FIG. 1 shows a generalized view of the side elevation of a transporttruck supporting the vibrator of this invention.

FIG. 2 shows a transverse section taken along the plane 2-2 of FIG. 1.

FIG. 3 shows a horizontal section taken along the plane 3-3 of FIG. 2.

FIG. 4 shows a horizontal section taken along the plane 4-4 of FIG. 2.

FIG. 5 is a side elevation taken along the plane 55 of FIG. 2.

FIGS. 5A and SB illustrate details of pistons and clamps.

FIG. 6 is a plan view taken along the horizontal plane 66 of FIG. 2.

FIG. 7 illustrates an alternate embodiment of a clamping mechanism.

FIG. 8 illustrates an embodiment of this invention utilizing twodouble-acting pistons and cylinders.

FIG. 9 illustrates a way to positively synchronize the valves oncylinders which are spacially separated from each other.

FIG. 10 illustrates a method of minimizing leakage of pressure fluidfrom the cylinders past the pressure seals.

FIG. 11 illustrates a closed, series, hydraulic drive for DESCRIPTION OFTHE PREFERRED EMBODIMENTS Referring now to the drawings, the numeral 10,represents generally the hold-down apparatus, numeral 11 representsgenerally the truck transport vehicle, numeral 12 represents generallythe vibrator lifting apparatus, the numeral 14 represents generally thevibrator system, numeral 16 the second frame for supporting the mass,and numeral 18 the mechanism that clamps the second frame to the truck.

The vibrator system 14 is mounted on a baseplate 20 which is supportedfrom the vehicle 11 by lifting means 12. The lifting means 12 comprisesa cylindrical rod 24 which is slidably received in a vertical guide tube29, fastened to the truck frame at its lower end. The rod 24 has acrossarm 26 at its bottom end which is attached to the compliances 22which are attached to the baseplate 20. The rod 24 at its upper endsupports two piston rods 30 which slide in hydraulic cylinders 28, 28',which are attached (FIG. 2) by means 35 to the frame 62 of the truck. Bypulling down on the piston rods 30, the rod 24 is forced down until thebaseplate hits the surface 17 of the earth 19. If the rods 30 are pulleddown farther, the truck body will be lifted until two of the wheels 23are off the ground, and part of the weight of the truck will besupported on the compliances 22 pressing down on the baseplate 20. Thispiston of the apparatus is well known in the art and forms no part ofthis invention.

The vibrator system illustrated in FIGS. 2-5 comprises four cylindersequipped with single-acting pistons 32, 32, 34, 34'. These arepositioned in the corners of a rectangle. Cylinders 32, 32 are on onediagonal. The other two cylinders 34, 34' are on the second diagonal.Pistons 36 in cylinder 32, and 36 in cylinder 32 are adapted to movedownwardly with respect to their cylinders on the application ofpressure fluid. The pistons 38 and 38 in cylinders 34 and 34respectively are adapted to move upwardly with respect to the cylinderson the application of pressure fluid.

The single-acting pistons can be simple rods inserted and sealed intothe cylinders. At the expense of more seals, the pistons (for example 36in FIG. 5A) can have a smaller diameter extension (36A). This permitsmore firm attachment of the pistons to the first frame 40 which ties thepistons to the baseplate.

On the other side of the drive shaft is a second set of pistons andcylinders identical to the two just described and shown in FIG. 5.However, on the opposite side (right side of the truck), the forwardpiston 36 moves downwardly, while on the left side the forward piston 38moves upwardly, and vice versa for the rearward pistons.

The cylinders (FIG. 5) 34 and 32 are joined to a second frame 16, whichhas upstanding legs 44 which support plate 46, which ties together thetwo sets of two cylinders. The first frame 40 may have cross arms (notshown) which tie together the two sets of pistons for greater rigidity.The total force of the pressure fluid acts on the pistons and throughthem to the frame 40 and thus to the baseplate and to the earth. Verylarge forces are generated and the frames 40 and 16 must be sufficientlyrigid to transmit this force without deformation. For simplicity andclarity of drawings, only simple frames are shown, although thoseskilled in the art will know how to design strong structural frames forthis purpose.

This design of vibrators differs in a number of respects from theconventional prior art devises which utilize a single cylinder, which isformed inside of the cylindrical mass and has a double-acting pistonsystem. Furthermore, these prior art vibrators are mounted high on topofa structural steel tower. The frame which supports the piston rods,and the tower are massive because the pistons rods must be commensuratewith the size of the mass, etc. In this design the pistons are singleacting so that the length of the piston rods is short and the firstframeis short. There is no tower, and thus the overall mass of themoving system is a minimum.

If desired, the second frame 16 can support a separate discrete volumeof metal, such as a cube, that would rest upon and be fastened to thehorizontal plate 46. However, in this invention the preferred embodimentinvolves the use of part of the mass of the vehicle as the reaction massfor the vibrator. This is illustrated in FIGS. 2, 5 and 6. A long rigidvertical post 48 is supported from the plate 46 of the second frame 16.When the baseplate is pressed into intimate contact with the earth, thepost will extend up through an opening 66 in the bed of the truck. Aplurality of horizontal hydraulic rams 56 (two of which are shown) are.slidable in cylinders 54 which are attached rigidly to the bed of thewith the electrical signal to the valve control system. These systemswork well when, as in the prior art, there is only a single vibrator.Whenthere are two or more vibrators, each mounted on separate trucks,then each vibrator requires the same feedback control to maintain thephase of each of the vibrators in constant phase relation with theelectrical signal, and therefore in constant phase relation with eachother.

The principal difference between this invention and the prior artdevices, is that there are more than a single cylinder, and thisvibrator system may contain two or more vibrators, each having acylinder and a piston. These are spaced apart on the baseplate. Tomaintain them in proper phase relation it is important that the valveswhich control the flow of pressure fluid are held precisely in-phase.This I do, by physically restricting and controlling the motion of thesevalves by tying them together with a mechanical or hydraulic system. Oneform of such a mechanical control system is shown in FIG. 9.

A hydraulic actuator 100 has a cylinder 101 and a piston 102 with twopiston rods 103, 104. Pressure fluid is introduced cyclically into thecylinder in accordance with an electrical signal by electrohydrauliccontrol means well known in the art. Such electrohydraulic controls areavailable on the market and need no further description. Shown are twopressure fluid control valves 112, 114 which are to be maintained inconstant phase relation with the actuator 102 to control pressure fluidflow to the two cylinders (not shown) as is well known in the art. Eachof the valves includes a cylinder 113 and a valve spool 116, fluidconnection to the vibrator cylinder 120, and fluid connection 121, 122to the pressure fluid high and low pressure reservoirs, not shown. Thepiston rods 103, 104 of the actuator 100 are connected by flexibletension cables 106 to the piston rods 117, 118, etc. of the valves 112,114, etc. by means of pulleys 108-111, etc. to provide a closed tensioncircuit. With suitable tension in the system and a minimum of stretch inthe cable 106, and a minimum ofmass in the valve spools 116, they willmove exactly in-phase with the piston of the actuator 100.

In order to ensure that all of the slack is out of the tension cable106, pulleys 123, 124, 125 may be used in conjunction with screw 126attached to the shaft of pulley 125, bracket 127 attached to the frameof the vibrator and nut 128 to maintain a static tension in the cablegreater than the alternating forces applied by the piston 102.

A similar synchronizing control system, can be designed in whichhydraulic liquid is used as the control medium in place of the tensioncable 106.

The operation of the spool valves in FIG. 9 is well known in the art andneed not be described further. Although only two valves are shown, asmany valves as desired can be connected through series cables, rods orhydraulic conduits and actuators, so that they are forced to operate inconstant phase with each other.

Although the details have not been described in this application, itwill be clear that the well known control systems using displacement orvelocity sensors on the baseplate and on the piston cylindercombinations to control the phase of the baseplate in synchronism withthe signal applied to the vibrator, can be used with the vibrator systemof this invention. In the prior art such control systems have beenapplied only to the single piston-cylinder systems. With the use of thevalve phase controls as described in conjunction with FIG. 9, it is notnecessary to provide duplicate electronic control systems and sensors oneach vibrator. Only one such control system would be needed since all ofthe valves and thus all of the vibrators would operate preciselytogether. Thissingle control could be applied to one of the plurality ofvibrators, or it could be applied between the first and a second frame,which respectively are fastened to the baseplate and the mass.

In the prior art vibrators with a single cylinder and two piston rods,certain volumes of liquid at a selected pressure are required togenerate the desired force. Using present day valve art, there is alimit to the volume of lquid which can be controlled by the valves as afunction of frequency. This limitation sets an upper limit on thefrequency of operation. In this invention, because only half as muchvolume is required for each cylinder, with the same valves, a muchhigher frequency of operation is possible. This feature combined withthe lower mass of the moving system provides a higher frequency vibratorthan the prior art systems.

FIG. 10 indicates a detail of the piston and cylinder construction whichrelates to the sealing of the pistons in the cylinders. The piston 168is fastened to the baseplate 170. The cylinder 164 is fastened to thesecond frame which is fastened to the mass. High pressure hydraulicliquid is applied to cylinder chamber 169 through pipe 177, valves 176,182 and through pipe 174. At the same time the pressure fluid is appliedthrough pilot pipe 178 and through the opening 180 through the cylinderwall, in the space between the two O-ring seals 165, 166. Thus, in thevery thin annular space between the piston and cylinder there is ahydraulic pressure which is, at all times, the same as that in thecylinder chamber 169. Thus there is no pressure difference across theseal ring 166 and therefore no leakage across that seal ring. Ifdesired, the pipe 178 can alternatively be connected through pipe 178 tothe source of pressure fluid through pipe 177. With the pipe 178connected to pipe 177 and maximum pressure applied to pipe 174, thevalve 182 can be closed and thereafter there will be no leakage ofpressure from chamber 169. This feature can be used in connection withthe cylinders and pistons of the clamping means described in connectionwith FIG. 7.

While I show clamping means for releasably clamping the second frame,through post 48 to the truck frame that operates on the basis ofhydraulic force, it is clear that motor driven screw means can of coursebe equally well used. The pistons and cylinders of FIGS. 6, 7, are, ineffect, hydraulic jacks, and motor driven screw jacks, or equivalentmeans, could be substituted for them.

In FIG. 11 is illustrated a hydraulic system that obviates the need ofvalves on each cylinder. Since the pistons are all connected to a rigidfirst frame 196, fluid flow through pipe 214 into cylinder chamber 216will drive piston 193 downwardly, and with it, the first frame 196,attached to baseplate 20. As the frame 196 moves down, piston 194presses fluid out of chamber 218 into pipe 220. Now, if piston 212 incylinder 210 is moved to the left, it will force liquid from chamber 213into pipe 214, and chamber 216, and will accept fluid from chamber 218through pipe 220 into chamber 222. The piston 222 can be driven throughpiston rod 202 by piston 201 in actuator cylinder 200. Piston 201 isdriven by pressure fluid controlled by valve means truck by clamps 68and bolts 70 (FIGS. 5 and 6) or by other means well known in the art.The rams are oriented radially toward the post 48. In this embodimentthe post 48 is shown as of square cross-section. It is convenienttherefore to use 2, or 4 rams, one directed against each face of thepost. The surfaces of the post are knurled or roughened 52, or havethreads, or V notches (FIG. 5B) etc., cut into the post, with matchingsurfaces on the faces of the rams 56. It is possible also, though notshown, to have two upright posts adjacent the frame post 48, the formerfastened securely to the bed of the truck, with a tapered horizontalopening formed through the three contiguous posts. The ram then wouldhave a tapered rod of the same taper, which would be inserted andpressed tightly into the tapered seat, to securely lock the masssupporting post to the truck frame.

Because there may be slight misalignments due to irregularities in thesurface on which the base plate rests, the faces of the rams, etc., andthe tapered rod could be on a swivel or ball-and-socket mechanism so asto adjust to the precise position of the baseplate and vibrator. Shownin FIG. 5B are ball and socket means 58 in the ends of the rams. Thesecan be held in place for example by rings 59 attached to the rams 56.

After the baseplate is placed on the earth, part of the weight of thetruck is applied through compliances 22, by lifting the rear end of thetruck, as is well known in the art. The rams 56 are then closed, atlight fluid pressure, until all of the rams are in contact with the post48. This light fluid pressure serves to position all pistons in contact,without disturbing the natural position of the post 48. Then the fluidpressure is increased until the pistons are pressed very tightly againstthe post. In this condition, because of the roughness of the post andpiston faces, there will be no slippage of the post with respect to thepistons. And, since the cylinders are securely anchored to the truckframe, the truck mass now becomes the reaction mass for the vibrator.

There may be some natural flexibility in the frame of the truck. Thismay have to be reinforced with stiffening members, to provide a rigidmass. It is possible also to combine a small mass (such as the secondframe itself, or the second frame plus a small mass) directly connectedto the cylinders, and the large mass of the truck. This can be a directconnection or with controlled compliances between the small mass and thetruck (which could be in the truck frame itself). Of course there willbe small resonances of piping and frames on the truck itself which mightrespond to the impressed oscillatory forces. These can be reinforced orisolated as is well known in the art. The compliance in the connectionbetween the post 48 and the truck (if present), might be designed toprovide an overall response to the system to improve the wave shape ofthe seismic signal generated in the earth.

It will be clear, that while I show the first frame, which is attachedto the baseplate, also attached to the pistons, and the second framewhich is attached to the mass also attached to the cylinders, this is amatter of choice, and the pistons could just as well be connected to thesecond frame, and the cylinders to the first frame. The choice ispreferably made so that the mass of the moving system is the leastpossible. Since the pistons are of smaller mass than the cylinders theyshould be connected to the first frame. Also, as will be discussedlater, the valves which control the pressure fluid should be attached tothe cylinders, and they should be attached to the mass, so as to have aslittle movement as possible.

Also, while I show a square post 48, a post of any number of faces(three or more) or a round post could be used with appropriate numbersof rams and corresponding shapes of clamping faces of the rams.

In FIG. 7 I show another embodiment of a clamp means for removablyattaching the second frame to the truck. This shows the post 48 with asphere 72 adjustably attached to the post, such as by threads, notshown. There are two spherical-seat plates 75, 76 above and below thesphere. These are held lightly together and to the sphere by bolts 89and springs 90. There is a structural frame 78 attached to the truckframe 60, and a plurality of vertical cylinders 80, 82 and pistons 84,86 below and above the plates 75, 76. There should be two sets of atleast three cylinders and pistons spaced angularly about the post 48.The upper and lower pistons are preferably in alignment.

In operation, after the baseplate is set and the truck lifted, the lowerpistons 84 are raised and the upper pistons 86 are lowered, byintroducing low pressure fluid through valves 91 and 88. When they areall in firm contact with the upper and lower plates 75, 76, the pressureis raised. When full pressure has been applied, there is still a smallgap 77 to permit the full pressure to be applied to the sphere and thepost. Then valves 88 and 91 are closed. The post 48 is now locked toframe 78 and to the bed of the truck.

Other means can, of course, be used to removably clamp the second frameof the vibrator to the truck frame. An important feature of thisinvention lies in the use of such releasable or removable clamping meansto obviate the need of a separate, discrete, heavy, costly reaction massfor the vibrator. It is also clear that a removable clamping means isrequired, which is released at all times except when the vibrator isoperating. A continuously applied clamping means cannot be used sincethe spacing between vibrator and truck is different when the vibrator israised for transport, and lowered for operation.

While my preferred embodiment is to use 4 cylinders and pistons as shownin FIGS. 2, 3, 4, each of which are single-acting, and positioned two oneach side of the drive shaft, I contemplate also using two double-actingpistons in cylinders, one on each side of the drive shaft. This is shownschematically in FIG. 8. There are two cylinders 87 containing twopistons 85. Each piston has two piston rods 92, 93. These are attachedto a first frame 94 which is attached to the baseplate 20. The cylinders87 are attached to second frame 95, which has risers 44 which attach toplate 46 as in FIG. 2. The system of FIG. 8 can, of course, carry aseparate reaction mass mounted on plate 46, although preferably, theplate 46, through post means 48 is removably clamped to the truck frameto use the truck as the reaction mass. The driveshaft 64 operates in thespace between the cylinders.

In the prior art devices, a single cylinder and piston system has beenused, with a single valve assembly to simultaneously control the flow ofpressure fluid to opposite sides of the double-acting piston.Furthermore, special apparatus including displacement sensors andfeedback circuitry (not shown) are used to ensure that the phase of themovement of the baseplate is (within selected ranges) maintained inconstant phase relation through openings 204, 206 from high and lowpressure hydraulic reservoirs, as is used on prior art vibrators. Theclosed hydraulic system of piston 212 could be pressured up by meanssuch as pump 207, for example, to provide as tight a control of pistons193,194 as desired. Also by change in diameter of piston 212 withrespect to piston 201, a force multiplication on the pistons 193, 194can be achieved. Thus the system of FIG. 11 not only obviates the needfor separate valves on each cylinder it guarantees the in-phaseoperation of all pistons. While only two pistons and cylinders areshown, any number can be connected in series in this way.

While the invention has been described with a certain degree ofparticularity, it is manifest that many changes may be made in thedetails of construction and the arrangement of components. It isunderstood that the invention is not to be limited to the specificembodiment set forth herein, by way of exemplifying the invention,

2. The vibrator system as in claim 1 in which said mass means comprisesa separate discrete volume of metal supported by said second frame.

3. The vibrator system as in claim 1 in which said 5 mass meanscomprises at lesat part of the mass of said vehicle.

4-. The vibrator system as in claim 3 including means to removably clampsaid second frame means to said vehicle.

5. in an electrohydraulic vibrator system for generating seismic wavesin the earth, said system including a transport vehicle, a baseplate, avibrator system having a first of two relatively reciprocating partsfastened to a first frame fastened to said baseplate and the second ofsaid two parts supporting a second frame, and means on said vehicle forpressing down on said baseplate through compliances with a force equalto at least portion of the weight of said vehicle, and means toselectively apply high pressure fluid to said vibrator system,

but the invention is to be limited only by the scope of the improvementcomprising;

the attached claim or claims, including the full range of equivalency towhich each element or step thereof is entitled.

What is claimed is:

1. In an electro-hydraulic vibrator system for generating seismicsignals in the earth, said vibrator mounted on a vehicle and includingbaseplate a, and means to support said baseplate from said vehicle, saidsupport means including means to lower said baseplate to the earthssurface, and means including a compliant means for pressing down on saidbaseplate with a force equal to part of the weight of said vehicle, theimprovement, comprising;

a. four cylinders and four pistons means slidably and sealably receivedtherein, one in each of said cylinders, said cylinders spaced apart onsaid baseplate in the four corners of a rectangle; frame means b. firstframe means attached to said pistons, and second frame means attached tosaid cylinders, either ofsaid first or said second frame means attachedto 4 and supported by said base plate, the other of said first or secondframemeans attached to a reaction mass positioned above said cylinders,the axes of said cylinders directed perpendicular to said baseplate;

c. reaction mass means supported by said second frame means; and

(1. means to selectively direct high pressure fluid to said cylinders,the first two cylinders on a first diagonal axis adapted to move theirpistons upwardly on the application of pressure fluid, the second twocylinders on the second diagonal axis adapted to move their pistonsdownwardly on the application of pressure fluid, said pressure fluidapplied sequentially to said first two cylinders and then to said secondtwo cylinders;

whereby pairs of upward forces will be simultaneously applied to saidbase plate at the corners of said first diagonal axis and pairs ofdownward forces will be simultaneously applied at the corners of saidsecond diagonal axis, sequentially, as said pressure fluid is appliedsequentially to said first two and to said second two cylinders, saidpairs of upward and downward forces all equal to each other andcombining to form an oscillating vertical force applied to saidbaseplate at the center of said rectangle.

means to releasably rigidly clamp said second frame to said vehiclewhile said vibrator is operating and to unclamp said second frame fromsaid vehicle when said vibrator is not operating, whereby said 25 secondframe and said vehicle are forced to move in unison when said vibratoris operating and to move separately when said vibrator is not operating,whereby at least a portion of the mass of said vehicle acts as at leasta part of the reaction mass for said vibrator system.

6. The vibrator system as in claim 5 in which said vibrator systemincludes a single cylinder and a single double-acting piston therein,said piston rigidly connected to said baseplate and said cylinderreleasably 35 rigidly clamped to said vehicle.

7. The vibrator system as in claim 5 including a plurality of cylindersand including:

a. valve means associated with each of said plurality of cylinders tocontrol the admission and expulsion of high pressure fluid to and fromsaid cylinders; and

b. control means to control said valve means whereby the operation ofsaid plurality of valves is simultaneous.

8. The vibrator system as in claim 7 in which said control means ishydraulic.

9. The vibrator system as in claim 7 in which said control means ismechanical.

10. The vibrator system as in claim 5 in which said clamp meanscomprises;

a. vertical post means attached to said second frame,

and

b. a plurality of opposed hydraulic rams attached to said vehicle in ahorizontal plane directed inwardly radially to said post means tosecurely grasp said post and means to removably apply hydraulic pressureto said rams.

11. The vibrator system as in claim 5 in which said clamp meanscomprises:

c. clamp frame means attached to the truck frame;

d. a plurality of upwardly directed pistons in cylinders fastened tosaid clamp frame below, and a second plurality above said seat plate;and

e. means to apply high pressure liquid to said cylinders to press saidpistons on said top and bottom seat plates; and

f. valve means to lock said pressure liquid in said cylinders.

12. The vibrator system as in claim in which said clamp means comprises:

a. vertical first post means attached to said second frame;

b. second post means attached to the truck frame on second post mountedon each side of said first post;

c. transverse openings coaxial through said three posts, said opening ofa selected taper; and

d. tapered piston rod means of said selected taper operativelycontrolled be driven into said tapered opening.

13. The vibrator system as in claim 11 including two spaced seal ringsbetween said pistons and their cylinders, and means to apply to theannular space between each piston and its cylinder, between said twoseal 7 rings, a liquid pressure substantially equal to the pressure ofsaid liquid in said cylinders.

14. In an electrohydraulic vibrator system for generating seismic wavesin the earth, said system including a transport vehicle, a baseplate,and means on said vehicle for pressing down on said baseplate throughcompliances with a force equal to at least a portion of the weight ofsaid vehicle, and including a vibrator system comprising a plurality ofspaced-apart vibrator assemblies, each assembly comprising two elementsrelatively reciprocable with respect to each other, one element of eachassembly connected to a first frame and the second element of eachassembly connected to a second frame, one frame connected to saidbaseplate, the other frame connected to a reaction mass, the improvementcomprising;

a. high pressure fluid means to operate said vibrator assemblies;

b. plurality of valve means, one associated with each of said vibratorassemblies for controlling the flow of pressure fluid to said vibratorassemblies and c. control means to drive all of said valve means inprecise synchronism.

15. The vibrator system as in claim 14 in which said control meanscomprises mechanical means.

16. The vibrator system as in claim 1 in which said vehicle has acentral longitudinal drive shaft and said cylinders and pistons arepositioned two on each side of said drive shaft.

17 The vibrator system a sdn claiinfS in which said cylinders andpistons are positioned adjacent said base plate.

18. The vibrator system as in claim 1 including:

(a) valve means associated with each of said plurality of cylinders tocontrol the admission and expulsion of high pressure fluid to and fromsaid cylinders; and

(b) control means to control said valve means whereby the operation ofsaid plurality of valves is simultaneous.

said control means comprises mechanical means.

20. The vibrator system as in claim 31 in which said control meanscomprises hydraulic means.

2 1 The vibrator system as in claim 13 in which said vibrator systemcomprises two cylinders, each including a double-acting piston therein.

22. The vibrator system as in claim 13 in which said vibrator systemcomprises four cylinders arranged in the corners of a rectangle. eachcylinder containing a single-acting piston. two of the pistons adaptedto move upwardly and two adapted to move downwardly with respect to saidcylinders on the application of said pressure fluid.

23. The vibrator system as in claim 24 in which at least part of saidreaction mass includes a part of the mass of said vehicle; and includingmeans to releasably rigidly clamp said other frame to said vehicle.

24. The vibrator system as in claim 24 in which said control meanscomprises hydraulic means.

UNITED STATES PATENT OFFICE CETTFTCATE 0T QORECTTQN Patent No. V V mm Dd February 5:}22

l v t r( Daniel Silverman It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

change 1'31" to --l8--, change "13" to --5--. change "13" to --'5----ochange "24 to --l change "24" to "-14".

Claim 20 line Claim 21 line Claim 22 line Claim 23 line Claim 24 lineSigned and sealed this 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents I FORM po'wso 9' uscoMM-Dc 60376-P69 I 1.5. GOVERNMENT PRINTINGOFFICE: 1959 0-356-334,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PH Li -fit NODated F y 5 I Inventor(s) Daniel Silverman It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

change 1'31" to --l8--. change "13" to --5--. change "13" to --5--.change "2'4" to --l4--'. change 24" to --l Claim 20 line Claim 21 lineClaim 22 line Claim 23 line Claim 2 line Signed and sealed this 17th dayof September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents I FORM 0 (10-69) USCOMM-DC 60376-P6S 1 a U.S. GOVERNMENTPRINTING OFFICE: I9" 0-366-33

1. In an electro-hydraulic vibrator system for generating seismicsignals in the earth, said vibrator mounted on a vehicle and includingbaseplate a, and means to support said baseplate from said vehicle, saidsupport means including means to lower said baseplate to the earthssurface, and means including a compliant means for pressing down on saidbaseplate with a force equal to part of the weight of said vehicle, theimprovement, comprising; a. four cylinders and four pistons meansslidably and sealably received therein, one in each of said cylinders,said cylinders spaced apart on said baseplate in the four corners of arectangle; b. first frame means attached to said pistons, and secondframe means attached to said cylinders, either of said first or saidsecond frame means attached to and supported by said base plate, theother of said first or second frame means attached to a reaction masspositioned above said cylinders, the axes of said cylinders directedperpendicular to said baseplate; c. reaction mass means supported bysaid second frame means; and d. means to selectively direct highpressure fluid to said cylinders, the first two cylinders on a firstdiagonal axis adapted to move their pistons upwardly on the applicationof pressure fluid, the second two cylinders on the second diagonal axisadapted to move their pistons downwardly on the application of pressurefluid, said pressure fluid applied seQuentially to said first twocylinders and then to said second two cylinders; whereby pairs of upwardforces will be simultaneously applied to said base plate at the cornersof said first diagonal axis and pairs of downward forces will besimultaneously applied at the corners of said second diagonal axis,sequentially, as said pressure fluid is applied sequentially to saidfirst two and to said second two cylinders, said pairs of upward anddownward forces all equal to each other and combining to form anoscillating vertical force applied to said baseplate at the center ofsaid rectangle.
 2. The vibrator system as in claim 1 in which said massmeans comprises a separate discrete volume of metal supported by saidsecond frame.
 3. The vibrator system as in claim 1 in which said massmeans comprises at lesat part of the mass of said vehicle.
 4. Thevibrator system as in claim 3 including means to removably clamp saidsecond frame means to said vehicle.
 5. In an electrohydraulic vibratorsystem for generating seismic waves in the earth, said system includinga transport vehicle, a baseplate, a vibrator system having a first oftwo relatively reciprocating parts fastened to a first frame fastened tosaid baseplate and the second of said two parts supporting a secondframe, and means on said vehicle for pressing down on said baseplatethrough compliances with a force equal to at least portion of the weightof said vehicle, and means to selectively apply high pressure fluid tosaid vibrator system, the improvement comprising; means to releasablyrigidly clamp said second frame to said vehicle while said vibrator isoperating and to unclamp said second frame from said vehicle when saidvibrator is not operating, whereby said second frame and said vehicleare forced to move in unison when said vibrator is operating and to moveseparately when said vibrator is not operating, whereby at least aportion of the mass of said vehicle acts as at least a part of thereaction mass for said vibrator system.
 6. The vibrator system as inclaim 5 in which said vibrator system includes a single cylinder and asingle double-acting piston therein, said piston rigidly connected tosaid baseplate and said cylinder releasably rigidly clamped to saidvehicle.
 7. The vibrator system as in claim 5 including a plurality ofcylinders and including: a. valve means associated with each of saidplurality of cylinders to control the admission and expulsion of highpressure fluid to and from said cylinders; and b. control means tocontrol said valve means whereby the operation of said plurality ofvalves is simultaneous.
 8. The vibrator system as in claim 7 in whichsaid control means is hydraulic.
 9. The vibrator system as in claim 7 inwhich said control means is mechanical.
 10. The vibrator system as inclaim 5 in which said clamp means comprises; a. vertical post meansattached to said second frame, and b. a plurality of opposed hydraulicrams attached to said vehicle in a horizontal plane directed inwardlyradially to said post means to securely grasp said post and means toremovably apply hydraulic pressure to said rams.
 11. The vibrator systemas in claim 5 in which said clamp means comprises: a. spherical ballmeans supported by said second frame; b. spherical seat plates above andbelow said ball means; c. clamp frame means attached to the truck frame;d. a plurality of upwardly directed pistons in cylinders fastened tosaid clamp frame below, and a second plurality above said seat plate;and e. means to apply high pressure liquid to said cylinders to presssaid pistons on said top and bottom seat plates; and f. valve means tolock said pressure liquid in said cylinders.
 12. The vibrator system asin claim 5 in which said clamp means comprises: a. vertical first postmeans attached to said second frame; b. second post means attached tothe truck frame on second post mounted on each side of said first pOst;c. transverse openings coaxial through said three posts, said opening ofa selected taper; and d. tapered piston rod means of said selected taperoperatively controlled be driven into said tapered opening.
 13. Thevibrator system as in claim 11 including two spaced seal rings betweensaid pistons and their cylinders, and means to apply to the annularspace between each piston and its cylinder, between said two seal rings,a liquid pressure substantially equal to the pressure of said liquid insaid cylinders.
 14. In an electrohydraulic vibrator system forgenerating seismic waves in the earth, said system including a transportvehicle, a baseplate, and means on said vehicle for pressing down onsaid baseplate through compliances with a force equal to at least aportion of the weight of said vehicle, and including a vibrator systemcomprising a plurality of spaced-apart vibrator assemblies, eachassembly comprising two elements relatively reciprocable with respect toeach other, one element of each assembly connected to a first frame andthe second element of each assembly connected to a second frame, oneframe connected to said baseplate, the other frame connected to areaction mass, the improvement comprising; a. high pressure fluid meansto operate said vibrator assemblies; b. plurality of valve means, oneassociated with each of said vibrator assemblies for controlling theflow of pressure fluid to said vibrator assemblies ; and c. controlmeans to drive all of said valve means in precise synchronism.
 15. Thevibrator system as in claim 14 in which said control means comprisesmechanical means.
 16. The vibrator system as in claim 1 in which saidvehicle has a central longitudinal drive shaft and said cylinders andpistons are positioned two on each side of said drive shaft.
 17. Thevibrator system as in claim 16 in which said cylinders and pistons arepositioned adjacent said base plate.
 18. The vibrator system as in claim1 including: a. valve means associated with each of said plurality ofcylinders to control the admission and expulsion of high pressure fluidto and from said cylinders; and b. control means to control said valvemeans whereby the operation of said plurality of valves is simultaneous.19. The vibrator system as in claim 18 in which said control meanscomprises mechanical means.
 20. The vibrator system as in claim 18 inwhich said control means comprises hydraulic means.
 21. The vibratorsystem as in claim 5 in which said vibrator system comprises twocylinders, each including a double-acting piston therein.
 22. Thevibrator system as in claim 5 in which said vibrator system comprisesfour cylinders arranged in the corners of a rectangle, each cylindercontaining a single-acting piston, two of the pistons adapted to moveupwardly and two adapted to move downwardly with respect to saidcylinders on the application of said pressure fluid.
 23. The vibratorsystem as in claim 14 in which at least part of said reaction massincludes a part of the mass of said vehicle; and including means toreleasably rigidly clamp said other frame to said vehicle.
 24. Thevibrator system as in claim 14 in which said control means compriseshydraulic means.